Solution to:
Acquiring Animals

We know that, except four, all animals are horses.
That means that the number of horses is equal to the number of animals in the stable, minus four.

We know that, except four, all animals are cows.
That means that the number of cows is also equal to the number of animals in the stable, minus four.

We know that, except four, all animals are sheep.
That means that the number of sheep is also equal to the number of animals in the stable, minus four.

We do not know yet how many animals in total are in the stable, but it is clear that the amounts of horses, cows, and sheep are equal.

We know that, except four, all animals are horses.
The four animals that are not horses, have to be cows and sheep.
This means that the number of cows and sheep in the stable is four.
However, we already know that there are as many cows as sheep in the stable.
So, there are two cows and two sheep in the stable (together four).
And therefore there are also two horses in the stable.

Conclusion: peasant Anya has two horses, two cows, and two sheep in her stable.